1. Field of the Invention
The present invention relates to a countercurrent direct-heating-type heat exchanger, in more detail, to a countercurrent direct-heating-type heat exchanger that is able to suppress the drift in the case when a fluid to be heated is supplied, to prevent local abrasion of the members and also to carry out efficient heat exchange, wherein heat exchange is carried out, while making a fluid to be heated inflow from its top and outflow from its bottom, and at the same time, making a heating medium inflow from its bottom and outflow from its top. It should be noted that, the fluid to be heated is generally a material to be heated having fluidity including, for example, a slurry fluid containing solid components.
2. Description of the Prior Art
A heat exchanger, wherein heat exchange is carried out to a heating medium, has been conventionally employed as a means for heating a fluid to be heat.
A High Pressure Acid Leach using an autoclave, for example, has been employed as one of the wet process for smelting of an oxide ore containing nonferrous metals such as nickel and cobalt. In the above High Pressure Acid Leach, the above oxide ore is prepared firstly into particles of a mean diameter of 2 mm or less in a crushing step and a sieving step and then prepared into an ore slurry of a specified concentration of solid components in a slurry-production step. The above ore slurry is then charged to a leaching step and subjected to leaching treatment under leaching conditions such as temperature and pressure selected as necessary. Subsequently, the leachate separated from a leached residue is subjected to removal of impurity elements and then to recovery of the objective metals such as nickel and cobalt.
In order to keep the leaching ratio high in the above leaching step, a temperature of about 200 to 300° C. is usually selected as the leaching condition in an autoclave. On the other hand, because the ore slurry produced in the previous step is usually prepared under a temperature condition of around outdoor temperature, the ore slurry not only lowers the temperature in the autoclave but also makes stable leaching reaction difficult when it is charged to the autoclave as it is. It is necessary, therefore, to make stepwise the temperature of the ore slurry close to temperature in the autoclave by preheating the ore slurry. In this time, when the ore slurry is simply heated in order to raise stepwise the temperature of ore slurry, the fluidity of ore slurry deteriorates as the water in the ore slurry evaporates, resulting in insufficient leaching reaction in the autoclave. Consequently, a device for preheating an ore slurry in actual operation of the above High Pressure Acid Leach is required to heat so as to keep the water content of ore slurry in good condition in order to suppress the fluidity deterioration of ore slurry.
Incidentally, various methods have been conventionally disclosed as a device for heating high-efficiently and stably a material such as a slurry. Examples include a horizontal rotary device equipped with a cylindrical vessel having the double side walls and many ejecting holes, in order to rotate the cylindrical vessel horizontally and eject a gas such as steam for heating into the vessel (for example, see Patent Literature 1) and a multi tube circular tube heat exchanger for heating a coal-water slurry, wherein the heat exchanger is installed so that the heat exchanging tube bundles become vertical direction, and the coal-water slurry flows downward in the heat exchanger tubes, and also a heat source fluid flows outside the relevant heat exchanger tubes (for example, see Patent Literature 2). These devices, however, usually have a problem that mechanical failures of the driving unit occur frequently or that indirect heating makes the structure of the device complicated, and thus are not always suitable as the heating method that satisfies the condition for heating while keeping its water content of ore slurry in good condition as described above, in a smelting plant where a large amount of ore material is treated, like the above wet process of smelting. By this reason, a countercurrent direct-heating-type heat exchanger, which has a simpler structure where steam is used as the heating medium, and the heating medium and the fluid to be heated flow counter-currently and are subjected to direct contact, has been employed.
The above countercurrent direct-heating-type heat exchanger is usually a type that heat exchange is carried out, while making a fluid to be heated inflow from its top and outflow from its bottom, and at the same time, making a heating medium inflow from its bottom and outflow from its top. In order to improve the contact between the fluid to be heated and the heating medium and thus to attain efficient heat exchange, the inside of main body of the above heat exchanger is equipped with umbrella-type dispersing plates for improving the dispersibility of the fluid to be heated flowing downward at its center and ring-like straightening plates for straightening the flow of the heating medium flowing upward on the side wall of the main body.
In operation of a countercurrent direct-heating-type heat exchanger in the actual operation the above High Pressure Acid Leach, an ore slurry is charged to the feed pipe installed horizontally at the top of the main body of the relevant heat exchanger and supplied to the apex part of the above umbrella-type dispersing plate from the feed nozzle which is connected with the relevant feed pipe and has an opening at the lower end in the vertical direction. The supplied ore slurry substantially forms a uniform stream flowing downward radially on the slope of the umbrella-type dispersing plate and is discharged from the bottom of the relevant heat exchanger. On the other hand, contrary to the ore slurry, steam is supplied from the bottom of the heat exchanger and forms a zigzag stream flowing upward by the above ring-type straightening plates and umbrella-type dispersing plates and is discharged from the steam outlet at the top of the heat exchanger.
The countercurrent direct-heating-type heat exchanger having such a structure is suitable as a preheating equipment in actual operation because direct contact of an ore slurry and steam flowing counter-currently makes it possible to heat the ore slurry while keeping its water content in good condition and also because the exchanger does not need the mechanical driving parts such as a motor or a pump and thus is free from troubles caused by the mechanical failures of the driving parts. Typical equipment trouble that occurs on a regular basis, however, includes an abrasion of each internal member due to the ore slurry. As for such an abrasion, as long as the flow of ore slurry forms substantially a uniform stream flowing downward radially on the slope of the umbrella-type dispersing plate, abrasion of the internal members such as the umbrella-type dispersing plates and the ring-type straightening plates develops uniformly as a whole and thus does not cause an unpredictable trouble such as degradation of the performance. That is, it is possible to confirm the degradation of such abrasion and performance in periodical inspections and then plan the renewal of equipment according to the plan.
However, there has been a problem that an ore slurry and steam begin to leak unexpectedly through a hole generated in the side wall of the main body of a countercurrent direct-heating-type heat exchanger or that local decrease in thickness of the relevant side wall is found in a large-scale periodical inspection accompanied by shutdown of operation to be conducted usually every half a year. It is considered that this phenomenon is caused by that the flow of the ore slurry supplied from the feed nozzle drifts to a specified direction on the umbrella-type dispersing plate and hits intensively a the side wall on specified part which is located on the extension line from the top face of the umbrella-type dispersing plate. The above situation, especially the outbreak of unexpected leak, requires great cost and time for repairing the relevant damaged part and causes not only the shutdown of the preheating step but also substantial reduction of the plant utilization rate in the whole operation of smelting. In addition, when the ore slurry drifts, the contact area between the ore slurry and steam becomes smaller than the area when the ore slurry forms a uniform stream flowing downward radially on the slope of the umbrella-type dispersing plate, which results in reduced efficiency of heat exchange and increased operation cost.
As described above, in a countercurrent direct-heating-type heat exchanger, technology for suppressing the drift of a fluid to be heated has been required from the standpoints of the life of equipment, and the efficiency of heat exchange with a heating medium and further the efficiency of the whole operation of smelting.    [Patent Literature 1] JP-A-6-238160 (page 1, page 2)    [Patent Literature 2] JP-A-5-26429 (page 1, page 2)